In the nuclear power industry, the nuclear energy source is in the form of hollow zircaloy tubes filled with enriched uranium, known as fuel assemblies. Upon being deleted to a certain level, spent fuel assemblies are removed from a reactor. At this time, the fuel assemblies emit extremely dangerous levels of neutrons and gamma photons (i.e., neutron and gamma radiation). It is necessary that the neutron and gamma radiation emitted from spent fuel assemblies be adequately contained at all times upon being removed from the reactor. Because water is an excellent radiation absorber, spent fuel assemblies are typically submerged under water in a pool promptly after being removed from the reactor. The pool water also serves to cool the spent fuel assemblies, which can initially give off dangerous amounts of heat that must be drawn away from the fuel assemblies.
Fuel storage racks that hold a plurality of spent fuel assemblies are typically used to support the spent fuel assemblies in the underwater environment of the pool. It is generally desirable that fuel storage racks support the fuel assemblies in a vertical orientation. Each fuel assembly is placed in a separate cell so that the fuel assemblies are shielded from one another. The cells are usually elongated vertical cavities which are open at their top ends for receiving the fuel assembly during a loading procedure. An example of a typical existing fuel rack, is described in U.S. Pat. No. 4,382,060, to Maurice Holtz et al., issued May 3, 1983, the entirety of which is hereby incorporated by reference.
During a typical underwater loading procedure of existing fuel racks, an empty fuel rack is first submerged in a fuel pool. The fuel rack must be sufficiently tall so that its cells can receive the entire length of the fuel assemblies to be loaded therein. Initially, a fuel assembly is positioned above the fuel rack in a vertical orientation and in alignment with the cell into which it will be loaded. Once the proper alignment is achieved, the fuel assembly is lowered into the cell. The fuel assembly maintains a vertical orientation during the entire loading process. For safety purposes, the entire fuel assembly must remain submerged within the water of the pool at all times. Thus, the depth of the pool must at a minimum be equal to the combined height of the fuel rack and the height of the fuel assembly (plus a margin of safety).
This minimum depth requirement for the underwater loading procedure presents problems for a number of facilities. In some instances, the fuel pool itself may not be deep enough to accommodate the combined height of the fuel rack and the fuel assembly. In other instances the temporary holding pools may not be adequately deep to perform the loading procedure in a safe manner.